The present invention relates to a scanning light source especially suited for incorporation in an exposure system of an electrostatic copying machine.
In a typical copying machine, an original document which is to be reproduced is placed face down on a transparent document carrier or platen. A light source comprising an elongated lamp and a reflector is disposed below the platen and radiates a narrow elongated beam of light onto the document. The carrier and document are moved perpendicular to the beam so that the document is progressively illuminated, for example, from top to bottom. An optical system focusses an image of the illuminated portion of the document onto a drum provided with a surface layer of a photoconductive material such as selenium or zinc oxide, the surface speed of the drum being equal to the surface speed of the document. As a result, an electrostatic image of the document is formed on the drum which is developed and transferred to a copy sheet to provide a permanent reproduction of the document.
In order to provide sufficient light intensity to properly expose the photoconductive drum, the lamp must be quite powerful, and unavoidably generate a substantial amount of heat. In a system in which the lamp and reflector are moved while the document is maintained motionless, the lamp is cooled through convection as a consequence of movement through the air. However, in the present system in which the document is moved while the lamp and reflector remain motionless, the lamp may generate enough heat to damage various parts of the copying machine or even start a fire if subjected to prolonged continuous operation. In addition, the life of the lamp is reduced considerably by the excessive heat.
It is known in the prior art to cool the lamp by means of a blower. However, a design choice has heretofore had to be made as to whether to provide a simplified arrangement in which the blower partially obstructs the light beam or a complicated and expensive arrangement including various ducts which avoids obstruction of the light beam.